Elucidating the Mechanism of Oxygen Reduction for Lithium-Air Battery Applications

Laoire, Cormac O.; Mukerjee, Sanjeev; Abraham, K. M.; Plichta, Edward J.; Hendrickson, Mary

doi:10.1021/jp908090s

Cited by 645 publications

(732 citation statements)

References 13 publications

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“…As previously determined, 33,34 the O 2 is first bound to the cathode surface via the oxygen vacancies, especially on the carbon defect sites and Au NC catalyst, followed by reduction to O 2 − . The stabilized superoxide ion could be combined via the dismutase reaction to form Li 2 O 2 .…”

Section: Mechanism Of LI 2 O 2 Formationsupporting

confidence: 52%

Gold nanocrystals with variable index facets as highly effective cathode catalysts for lithium–oxygen batteries

Dou

Wang

2015

NPG Asia Mater

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Cathode catalysts are the key factor in improving the electrochemical performance of lithium-oxygen (Li-O 2 ) batteries via their promotion of the oxygen reduction and oxygen evolution reactions (ORR and OER). Generally, the catalytic performance of nanocrystals (NCs) toward ORR and OER depends on both composition and shape. Herein, we report the synthesis of polyhedral Au NCs enclosed by a variety of index facets: cubic gold (Au) NCs enclosed by {100} facets; truncated octahedral Au NCs enclosed by {100} and {110} facets; and trisoctahedral (TOH) Au NCs enclosed by 24 high-index {441} facets, as effective cathode catalysts for Li-O 2 batteries. All Au NCs can significantly reduce the charge potential and have high reversible capacities. In particular, TOH Au NC catalysts demonstrated the lowest charge-discharge overpotential and the highest capacity of~20 298 mA h g − 1 . The correlation between the different Au NC crystal planes and their electrochemical catalytic performances was revealed: high-index facets exhibit much higher catalytic activity than the low-index planes, as the high-index planes have a high surface energy because of their large density of atomic steps, ledges and kinks, which can provide a high density of reactive sites for catalytic reactions. INTRODUCTIONThe lithium-oxygen (Li-O 2 ) battery is currently the subject of much scientific investigation as the power source for electric vehicles because of its high energy density (2-3 kWh kg − 1 ). 1 Unlike the intercalation reactions of Li-ion batteries, 2 the reaction mechanism in a Li-O 2 cell involves an oxygen reduction reaction (ORR) in the discharge process and an oxygen evolution reaction (OER) in the charge process, during which, molecular O 2 reacts reversibly with Li + ions (Li + + O 2 +2e − ↔ Li 2 O 2 , with an equilibrium voltage of 2.96 V vs. Li). 3 The performance of Li-O 2 batteries is constrained by several serious issues, such as poor cycling stability, 4 electrolyte instability, 5 low-rate capability 6 and low round-trip efficiencies, 1 mainly resulting from the high overpotential on charge. 7 Recently, it was found that the catalyst and the proper non-aqueous electrolyte are the key factors to address these problems. 8 Therefore, various electrocatalysts, including carbons, metal oxides, metal nitrides and precious metals have been examined as the cathode catalysts in Li-O 2 cells to lower the charge overpotential. 9 It was reported that the use of catalysts can decrease the charge potential tõ 3.8 from~4.2 V. 10 It has been shown, however, that the theoretical overcharge potential for a Li 2 O 2 film is only 0.2 V, if there are no limitations on charge transport through Li 2 O 2 to the Li 2 O 2 -electrolyte interface. 11 Therefore, it is possible to further lower the charge potential. Moreover, a fundamental understanding of how to resolve the high overpotential on charge and the mechanisms of both ORR and OER, respectively in non-aqueous electrolytes are important for developing Li-O 2 batteries.

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Section: Mechanism Of LI 2 O 2 Formationsupporting

confidence: 52%

Gold nanocrystals with variable index facets as highly effective cathode catalysts for lithium–oxygen batteries

Dou

Wang

2015

NPG Asia Mater

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“…Furthermore, the VGNS on the Ni foam can facilitate the adsorption of oxygen molecules on the surface of graphene nanosheets because of the high surface area. As reported previously, 48,50 O 2 is first bound to the cathode surface via oxygen vacancies, especially on the carbon defect sites and Ru catalyst nanoparticles, followed by reduction to O 2 − . The stabilized superoxide ions could be combined via the dismutase reaction to form Li 2 O 2 .…”

Section: Resultssupporting

confidence: 64%

Ruthenium nanocrystal decorated vertical graphene nanosheets@Ni foam as highly efficient cathode catalysts for lithium-oxygen batteries

Seo

et al. 2016

NPG Asia Mater

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The electrochemical performance of lithium-oxygen (Li-O 2 ) batteries can be markedly improved through designing the architecture of cathode electrodes with sufficient spaces to facilitate the diffusion of oxygen and accommodate the discharge products, and optimizing the cathode catalyst to promote the oxygen reduction reaction and oxygen evolution reaction (OER). Herein, we report the synthesis of ruthenium (Ru) nanocrystal-decorated vertically aligned graphene nanosheets (VGNS) grown on nickel (Ni) foam. As an effective binder-free cathode catalyst for Li-O 2 batteries, the Ru-decorated VGNS@Ni foam can significantly reduce the charge overpotential via the effects on the OER and achieve high specific capacity, leading to an enhanced electrochemical performance. The Ru-decorated VGNS@Ni foam electrode has demonstrated low charge overpotential of~0.45 V and high reversible capacity of 23 864 mAh g − 1 at the current density of 200 mA g − 1 , which can be maintained for 50 cycles under full charge and discharge testing condition in the voltage range of 2.0-4.2 V. Furthermore, Ru nanocrystal decorated VGNS@Ni foam can be cycled for more than 200 cycles with a low overpotential of 0.23 V under the capacity curtained to be 1000 mAh g − 1 at a current density of 200 mA g − 1 . Ru-decorated VGNS@Ni foam electrodes have also achieved excellent high rate and long cyclability performance. This superior electrochemical performance should be ascribed to the unique three-dimensional porous nanoarchitecture of the VGNS@Ni foam electrodes, which provide sufficient pores for the diffusion of oxygen and storage of the discharge product (Li 2 O 2 ), and the effective catalytic effect of Ru nanocrystals on the OER, respectively. Ex situ field emission scanning electron microscopy, X-ray diffraction, Raman and Fourier transform infrared measurements revealed that Ru-decorated VGNS@Ni foam can effectively decompose the discharge product Li 2 O 2 , facilitate the OER and lead to a high round-trip efficiency. Therefore, Ru-decorated VGNS@Ni foam is a promising cathode catalyst for rechargeable Li-O 2 batteries with low charge overpotential, long cycle life and high specific capacity.

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“…However, several factors hamper the practical performance of current lithium-oxygen batteries. First of all, superoxide is formed as the first product of the reduction of O2: 8,9 O2 + e -+Li + → LiO2…”

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confidence: 99%

“…In addition, such catalysts would also be beneficial in order to speed up the overall 2-electron reduction of oxygen to Li2O2. In the absence of such catalyst, Li2O2 is usually formed by disproportionation of LiO2: 8,9 2LiO2 →O2+ Li2O2 (3) However, as will be shown below, the rate of this reaction is very slow at low superoxide concentrations. Another important issue in lithium-oxygen batteries is that the discharge product, Li2O2, deposits on the surface of the electrode, blocking its electrochemical activity.…”

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confidence: 99%

A new method to prevent degradation of lithium–oxygen batteries: reduction of superoxide by viologen

et al. 2015

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Lithium-oxygen battery development is hampered by degradation reactions initiated by superoxide, which is formed in the pathway of oxygen reduction to peroxide. This work demonstrates that the superoxide lifetime is drastically decreased upon addition of ethyl viologen, which catalyses the reduction of superoxide to peroxide.Lithium-oxygen batteries can potentially deliver 5 times more energy than lithium-ion batteries of the same weight. [1][2][3][4][5][6][7] The energy is provided by the electrochemical reaction between Li and O2, typically forming Li2O2. Since all these compounds are very light, the mass of the battery can be very small, leading to a high specific energy (i.e. energy per mass). However, several factors hamper the practical performance of current lithium-oxygen batteries. First of all, superoxide is formed as the first product of the reduction of O2: 8,9 O2 + e -+Li + → LiO2(1) It has been shown that superoxide reacts irreversibly with most known electrolytes 10 and it is also probably involved in the corrosion of carbon electrodes. 11 Intensive research has been done on finding alternative electrolytes and electrode materials that are resistant towards degradation by superoxide. A few solvents like dimethyl sulfoxide 12 , some glymes 13, 14 and pyrrolidinium or piperidinium based ionic liquids [15][16][17][18][19] have been identified as promising electrolyte choices. Gold 12 and TiC 20 electrodes have shown much better capacity performance than carbon, in terms of cycling stability and suppression of side reactions. An alternative approach to solve the superoxide problem is the introduction of catalysts to promote the reduction of superoxide to peroxide: LiO2 + e -+Li + → Li2O2(2) This would decrease the lifetime of superoxide and, with this, the long-term durability of the battery. If the superoxide lifetime were short enough, it would be conceivable that a wider range of materials could be incorporated in lithium-oxygen batteries without serious problems of degradation reactions. In addition, such catalysts would also be beneficial in order to speed up the overall 2-electron reduction of oxygen to Li2O2. In the absence of such catalyst, Li2O2 is usually formed by disproportionation of LiO2: 8, 9 2LiO2 →O2+ Li2O2 (3) However, as will be shown below, the rate of this reaction is very slow at low superoxide concentrations. Another important issue in lithium-oxygen batteries is that the discharge product, Li2O2, deposits on the surface of the electrode, blocking its electrochemical activity. This produces a very early end of discharge, with little discharge product being formed, and little capacity being delivered. An innovative solution to solve this problem is the introduction of soluble redox shuttles that can displace the formation of Li2O2 from the electrode surface to the solution, by reducing oxygen through a homogenous chemical reaction. 21,22 Soluble redox couples have also been used as mediators for the evolution of oxygen in lithium-oxygen batteries, resulting in major performance i...

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Elucidating the Mechanism of Oxygen Reduction for Lithium-Air Battery Applications

Cited by 645 publications

References 13 publications

Gold nanocrystals with variable index facets as highly effective cathode catalysts for lithium–oxygen batteries

Gold nanocrystals with variable index facets as highly effective cathode catalysts for lithium–oxygen batteries

Ruthenium nanocrystal decorated vertical graphene nanosheets@Ni foam as highly efficient cathode catalysts for lithium-oxygen batteries

A new method to prevent degradation of lithium–oxygen batteries: reduction of superoxide by viologen

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